How did Messelson and Stahl experimentally prove that DNA replication is semiconservative? Explain.
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Experiment :
15N (heavy) and 14N (normal) are two isotopes of nitrogen which can be distinguished based on their densities by centrifugation in cesium chloride (CsCl). Meselson and Stahl cultured E.coli in a medium constituting 15NH4Cl over many generations. As a result, 15N was integrated into the bacterial DNA. Later, they revised the 15NH4Cl medium to normal 14NH4Cl. At a regular interval of time, they took the sample and checked for the density of DNA.
Observation :
Sample no. 1 (after 20 minutes): The sample had bacterial DNA with an intermediate density. Sample no. 2 (after 40 minutes): The sample contained DNA with both intermediate and light densities in the same proportion.
Conclusion :
Based on observations and experimental results, Meselson and Stahl concluded that DNA molecules can replicate semi-conservatively. Investigation of semiconservative nature of replication of DNA or the copying of the cells DNA didn’t end there. Followed by Meselson and Stahl experiment, Taylor and colleagues conducted another experiment on Vicia faba (fava beans) which again proved that replication of DNA is semiconservative.
15N (heavy) and 14N (normal) are two isotopes of nitrogen which can be distinguished based on their densities by centrifugation in cesium chloride (CsCl). Meselson and Stahl cultured E.coli in a medium constituting 15NH4Cl over many generations. As a result, 15N was integrated into the bacterial DNA. Later, they revised the 15NH4Cl medium to normal 14NH4Cl. At a regular interval of time, they took the sample and checked for the density of DNA.
Observation :
Sample no. 1 (after 20 minutes): The sample had bacterial DNA with an intermediate density. Sample no. 2 (after 40 minutes): The sample contained DNA with both intermediate and light densities in the same proportion.
Conclusion :
Based on observations and experimental results, Meselson and Stahl concluded that DNA molecules can replicate semi-conservatively. Investigation of semiconservative nature of replication of DNA or the copying of the cells DNA didn’t end there. Followed by Meselson and Stahl experiment, Taylor and colleagues conducted another experiment on Vicia faba (fava beans) which again proved that replication of DNA is semiconservative.
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